This invention generally relates to a process for attaching fittings to pipes prior to a brazing operation. With more particularity, this invention relates to the process for attaching fittings to pipes wherein an extruded fitting is machined from opposite sides to allow for inter-engagement with a corresponding fitting on one side and a pipe on the other.
Heat exchangers, radiators, evaporators, and condensers are typically manufactured from an alloy that is coated or clad with a thin surface layer of braze material which is then cycled through a braze oven to permanently join the parts together. It is common for pipes to be joined with such parts as, a condenser core utilizing the same braze oven that is used to braze the condenser core. The fittings and pipes are commonly provided, pre-brazed to each other as a pipe and block fitting assembly, by an outside supplier to be used as a component of the larger assembly, such as a condenser unit. It has been found that the originally formed joint between a pipe and a fitting will remelt and solidify, during the condenser core brazing operation. Problems can occur when the brazing alloy flows away from where it was intended and solidifies with less overlapping surface than is ideally desired. This less than desirable braze overlap is often of sufficient strength for the joint to successfully pass a quality check to detect leaks, but the weakened joint may then fail during the installation or attachment process in an assembly plant. It has been suggested to use a higher temperature braze alloy for the pipe to fitting attachment that would tend not to remelt during the condenser brazing operation. However, the fitting materials that are used for their desirable machining properties have a melting temperature that would be close in temperature to the higher melting temperature brazing alloys. Therefore, use of the higher melting temperature brazing alloys is not desirable, as it may cause the fitting itself to melt and lose its integrity during pipe to fitting attachment, prior to passing the pipes through the condenser brazing operation.
Accordingly, it is an object of the present invention to provide a method for maintaining the orientation of fittings to pipes without brazing them prior to a core brazing operation, to provide a geometry in which a strong braze overlap of the pipe to fitting is created in the final assembly braze process, such as the condenser core braze operation, while joint re-melt or deterioration is avoided. It is also an object of the present invention to provide a method of brazing fittings to pipes such that the orientation of the fitting and pipes can be maintained without the use of complicated brazing fixtures.
There is provided a process which cures those deficiencies outlined above and provides a reliable means to assure a quality fitting to pipe joint, as well as maintain the proper orientation of the parts. The process includes providing an extruded fitting which has a bore formed by the extrusion process extending from a first surface to a second surface, where the axis of the bore is approximately perpendicular to both of the first and second surfaces. The bore is then machined in both directions along the axis of the bore. The bore is machined from the first surface along the axis to form a ledge that will interact with a corresponding fitting. The bore is machined from a direction from the second surface along the axis for a distance that is less than the entire length of the bore, to provide a stop. A pipe having a braze collar placed circumferentially thereon is then inserted into the extruded fitting in a direction from the second surface to inter-engage the collar and the stop. The pipe and collar is then expanded using a mandrel to conform the shape of the pipe and collar to the bore. The assembled fitting is then brazed in a furnace to permanently attach the pipe to the extruded fitting.